1. Field of the Invention
The present invention relates to a scroll-type fluid displacement machine having a pair of rotating scroll bodies, which is used as a blower or a vacuum pump.
2. Prior Art
A known scroll-type fluid displacement machine has a pair of scroll bodies that rotate respectively around each central axis. The central axes are offset from one another. Scroll (spiral) vanes of one of the scroll bodies are angularly shifted from scroll vanes of the other scroll body. Such constructed vanes define compression chambers one after another, which are moved and lessened to compress the enclosed fluid when the pair of scroll bodies rotate synchronously.
In a first type of such displacement machines, which is most commonly used, one of the scroll bodies is driven by a prime mover, while the other scroll body is rotated by friction, since scroll vanes of the other scroll body contact with scroll vanes and a side plate of the one of scroll bodies.
In a second type of the displacement machines, there is provided a synchronous rotation mechanism having arms each connected to an outer periphery of a pair of scroll bodies and also an Oldham coupling associated with the arms for synchronously rotating the scroll bodies.
In a third type of the displacement machines, there is disposed an Oldham coupling around central axes of the scroll bodies for synchronously rotating the scroll bodies. The Oldham coupling may be supplied with lubricating oil or may be oil-free.
The first and second types of displacement machines drive the secondary scroll body by the frictional contact of the scroll vanes or of the synchronous rotation mechanism, which wears the scroll vanes or the rotation mechanism and generates a large metallic noise due to the frictional contact. In addition, these constructions require to supply lubricating oil to the friction parts.
In the third type of displacement machines, the Oldham coupling is positioned in a space around the center axes of the scroll bodies. The space is heated up by a high fluid temperature in an adjacent compression chamber of a high compression rate. Accordingly, the oil-supplied Oldham coupling may suffer sticking due to vaporizing of the lubricating oil or by thermal expansion of a torque transmission disc and shaft coupling members. Meanwhile, an oil-free Oldham coupling must be made of a material having a better performance in self-sliding capability, high-temperature resistance, and wear resistance when used in a continuous operation of the machine. It is difficult to get such materials.
Moreover, it has been desired that the pair of scroll vanes are of an oil-free type and do not contact with one another.